1. Field of the Invention
The present invention relates to an X-ray diagnosis apparatus with a function of X-ray fluoroscopy and a method of X-ray fluoroscopy, wherein X-ray fluoroscopic images are produced by X-rays generated intermittently.
2. Discussion of the Background
It is known that X-ray fluoroscopic images are obtained in an X-ray diagnosis apparatus. Recently, an X-ray fluoroscopy for such images has been achieved by radiation of an X-ray towards an object, such as a patient, in a form of a plurality of intermittent pulses. Such an X-ray is hereinafter referred to as an intermittent pulse X-ray, an intermittent X-ray pulse, or just simply an X-ray pulse. An auto brightness control (ABC) is known as a conventional technique to obtain an optimal or preferable brightness of an X-ray fluoroscopic image by the intermittent pulse X-ray radiation.
The ABC will be explained with reference to FIGS. 1 and 2. FIG. 1 is a block diagram showing an X-ray diagnosis apparatus according to a prior art. As shown in FIG. 1, the X-ray diagnosis apparatus generally includes an X-ray tube 10, a transmitted-X-ray detector 11, an integrator 12, and an X-ray control circuitry 20. The X-ray control circuitry 20 includes a comparator 13 and an X-ray condition-setting unit 14. The X-ray tube 10 radiates an X-ray towards a patient P. The transmitted-X-ray detector 11 detects an X-ray transmitted through the patient P as a result of the X-ray radiation by the X-ray tube 10. The integrator 12 integrates detected results obtained from the transmitted-X-ray detector 11. The comparator 13 compares an integrated result obtained from the integrator 12 to a reference value. The reference value is usually determined, in advance, to represent an optimal or preferable brightness of an X-ray fluoroscopic image. The X-ray condition-setting unit 14 sets and controls X-ray conditions of the X-ray radiation by the X-ray tube 10, such as an X-ray tube voltage, an X-ray tube current, and a pulse width of the intermittent pulse X-ray, based on a comparison result obtained from the comparator 13.
FIG. 2 is a diagram showing a conventional process of the ABC in the X-ray diagnosis apparatus according to the prior art. Responsive to activation of an X-ray radiation switch (foot switch) by an operator, the X-ray radiation begins for the X-ray fluoroscopy. The X-ray radiation is made with the intermittent pulse X-ray. In such an X-ray fluoroscopy, a brightness of an X-ray fluoroscopic image is optimized in the X-ray diagnosis apparatus shown in FIG. 1.
First of all, a first X-ray pulse (a first intermittent pulse X-ray) (a) is radiated to the patient P as shown in FIG. 2. The first X-ray pulse (a) is detected in the transmitted X-ray detector 11 and integrated in the integrator 12. The integrated X-ray data which represent a brightness of an X-ray fluoroscopic image are fed back to the comparator 13. In the comparator 13, the integrated X-ray data are compared to the reference value. The comparison result is fed to the X-ray condition-setting unit 14. A condition of a next X-ray pulse is determined according to the comparison result and is set for the X-ray tube 10. The condition to be determined includes, for example, an X-ray tube voltage, an X-ray tube current, and a pulse width of the X-ray pulse. The pulse width may often be fixed while the X-ray tube voltage and the X-ray tube current are usually changed in such a determination. Under the set condition, a second X-ray pulse (a second intermittent pulse X-ray) (b) is radiated to the patient P and a similar brightness control is performed as described above. By repeating such brightness control processes several times, a brightness of an X-ray fluoroscopic image to be obtained comes close to the reference value. Since a required X-ray pulse for the predetermined optimal or preferable brightness varies in response to a body movement of the patient P (this is because a thickness of the body to be X-ray transmitted is changed as the patient moves even slightly), the detected and integrated X-ray data are compared to the reference value in succession in the following X-ray pulses, such as X-ray pulses (c), (d), (e), and (f).
In the ABC, however, requires repetition of X-ray pulses radiation to obtain the optimal or preferable brightness of an X-ray fluoroscopic image. Accordingly, it usually takes time to reach such brightness and keep it stable through images. Particularly, when X-ray pulses are radiated intermittently at a low rate (radiated less often in a predetermined unit time), it is likely to happen to take tens of seconds to reach the optimal or preferable brightness. Further, such repeated radiation is obviously harmful to the patient P.